Multiple sclerosis (MS) is a neurodegenerative disease affecting approximately 2.5 million people worldwide and is the most frequent cause of disability in young adults. Balance and gait impairments are common in MS, however, the manifestation of balance and mobility impairments is variable depending on the set of neural processing disruptions in the particular individual with MS. Most kinematic and kinetic analyses of gait and balance in MS have thus far focused on individuals with minimal clinical disability. Rehabilitation to improve gait and balance in this population have shown results in 6-8 weeks of exercise therapy. A novel intervention, balance-based torso-weighting (BBTW), a weighting technique tailored to individual directional balance loss, has shown immediate improvements in balance and gait in people with MS. The weight added to the torso is minimal (<1.5% body weight) and strategically placed according to the person's imbalance. However, the mechanisms behind its immediate effectiveness remain mysterious, and recommendations regarding people with MS or other disorders that will benefit remain vague. For Specific Aim 1 of this study, we will perform kinematic and kinetic analyses of standing and walking with and without BBTW in people with MS and healthy controls. For Specific Aim 2 of this study, we will examine which of several impairments of the sensory and motor systems best predicts immediate improvement in balance and mobility with BBTW in a new sample of participants with MS compared to healthy controls. The research goal is to refine hypotheses regarding the mechanism behind BBTW intervention, and clarify who will receive the most benefit. Future research could then test the hypotheses generated from this work. If we achieve our two specific aims, we will have evidence to add to the scientific knowledge regarding the mechanism of light weighting as a sensory supplement to change strategies for postural control. This study will help us understand the mechanisms for responsiveness to BBTW, and possibly to other interventions that supplement sensory input. With that knowledge, we can develop more effective interventions for people with MS or other neural disorders, improving clinical outcomes and quality of life. If we can determine which patients are most likely to benefit from this type of intervention, health care delivery can be more efficient as well as effective. PUBLIC HEALTH RELEVANCE: By beginning to unravel the mechanisms behind light torso-weighting we can develop more effective interventions for people with MS or other neural disorders that impair balance and gait. Such interventions will improve clinical outcomes and quality of life. When we determine the patients most likely to benefit from this type of intervention, health care delivery can be more efficient as well as effective.